The present invention relates to a gas sensor for detecting a concentration of a gas component in a gas such as an exhaust gas emitted from an internal combustion engine. The present invention further relates to a method of producing such a gas sensor.
An example of gas sensor is disclosed in U.S. Pat. No. 5,859,361. The sensor includes a sensor element which is fixedly held in a housing by crimping.
A problem of the prior art gas sensor is that crimping of the housing varies from product to product, i.e., the position at which a cold crimped portion of the housing is bent varies from product to product, thus causing the cold crimped portion to vary in size. Such a variation of the size of the cold crimped portion causes a variation of the compressive force applied to insulators disposed between the housing and the sensor element and therefore a variation of the stress caused in the insulators, thus causing a variation in the seal between the sensor element and the housing.
In case the housing is of the kind having a hot crimped portion additionally, such a variation of the size of the cold crimped portion causes a variation of the size of the hot crimped portion, thus causing the same problem as described above.
It is accordingly an object of the present invention to provide a gas sensor which can prevent a variation of the size of a cold crimped portion of a housing from product to product and therefore a variation of the compressive force applied to insulators disposed between the housing and a sensor element, and thereby can provide a reliable seal between the sensor element and the housing.
To accomplish the above object, there is provided according to an aspect of the present invention a gas sensor comprising a sensor element for detecting a concentration of a gas component in a gas, and a housing having an accommodation hole in which the sensor element is disposed, the housing having at an axial end thereof a cold crimped portion which cooperates with a shoulder portion of the accommodation hole to fixedly hold therebetween the sensor element, the cold crimped portion having an inward flange section, a hollow cylindrical section and a bent section between the inward flange section and the cylindrical section, the cold crimped portion being shaped so as to vary in thickness suddenly at or adjacent the bent section.
According to another aspect of the present invention, there is provided a gas sensor comprising a sensor element for detecting a concentration of a gas component in a gas, and a housing having an accommodation hole in which the sensor element is disposed, the housing having at an axial end thereof a cold crimped portion which cooperates with a shoulder portion of the accommodation hole to fixedly hold therebetween the sensor element, the cold crimped portion having an inward flange section, a hollow cylindrical section and a bent section between the inward flange section and the cylindrical section, the cold crimped portion having at or adjacent the bent section an annular soft section which is smaller in hardness than a remaining part thereof.
According to a further aspect of the present invention, there is provided a method of producing a gas sensor including a sensor element for detecting a concentration of a gas component in a gas, and a housing having an accommodation hole in which the sensor element is disposed, the housing having at an axial end thereof a cold crimped portion which cooperates with a shoulder portion of the accommodation hole to fixedly hold therebetween the sensor element, the cold crimped portion having an inward flange section, a hollow cylindrical section and a bent section between the inward flange section and the cylindrical section, the method comprising preparing the housing having the cold crimped portion which is hollow cylindrical before being crimped, providing the cold crimped portion, before being crimped, with a section where the cold crimped portion varies in thickness suddenly, and crimping the housing in such a manner that the cold crimped portion has the bent section at or adjacent the section where the cold crimped portion varies in thickness suddenly.
According to a further aspect of the present invention, there is provided a method of producing a gas sensor including a sensor element for detecting a concentration of a gas component in a gas, and a housing having an accommodation hole in which the sensor element is disposed, the housing having at an axial end thereof a cold crimped portion which cooperates with a shoulder portion of the accommodation hole to fixedly hold therebetween the sensor element, the cold crimped portion having an inward flange section, a hollow cylindrical section and a bent section between the inward flange section and the cylindrical section, the method comprising preparing the housing having the cold crimped portion which is hollow cylindrical before being crimped, providing the cold crimped portion, before being crimped, with an annular soft section which is smaller in hardness than a remaining part thereof, and crimping the housing in such a manner that the cold crimped portion has the bent section at or adjacent the annular soft section which is smaller in hardness than the remaining part thereof.